(1) FIELD OF THE INVENTION
The present invention relates to a micro-image handling apparatus with an automatic focusing function.
(2) DESCRIPTION OF THE PRIOR ART
With a microreader having a printing function, which is also known as a microreader-printer, a clear reproduction of an original image becomes difficult due to defocusing which occurs with changing of certain elements such as a projecting lens for projecting the original image in magnification through an optical system, a microfilm and a film carrier. Such defocusing does not present a serious problem to a reading mode in which the original image is projected onto a screen, but is detrimental to a printing mode for printing out the original image. Accordingly, a focusing operation is carried out with the existing microreader-printer before printing the original image.
The printing of the original image is started when the operator presses a print button. Normally the operator presses the print button when he or she wishes to print the image, with little attention to whether the machine is in the focusing process at the time. The operator often presses the print button during the focusing process, which gives rise to a problem in the relationship between the focusing operation and the printing operation. That is, a well-focused image cannot be printed where the focusing operation in progress is terminated in favor of a printing operation. Conversely, if an operation of the print button is nullified during the focusing operation, the operator must press the print button again after waiting for completion of the focusing operation, which adds trouble to the printing operation.
Similar inconveniences have been noted of the focusing operation in relation to (a) frame searching, (b) changing of the microfilm carrier, and (c) changing of the lens. Reasons for such inconveniences will be discussed next.
(a) The microreader-printer also has a frame searching function for finding a desired frame among a multiplicity of frames recorded on a microfilm, and this function has the following problem with the focusing function. Conventionally, a frame search does not override a focusing operation in progress even when a search button is pressed. Although the necessity to search a frame may arise during a focusing operation, the operator must take the trouble of waiting for completion of the focusing operation and pressing the print button again. Besides, a great variety of original images are recorded on a microfilm, and projecting magnification must be varied frequently for projecting different images. Each time the magnification is varied, certain optical conditions must be changed including a change in the focal length of the zoom lens and turning of the image, which in turn requires a focusing operation to be carried out all over again. The focal point set prior to a frame search is often of no avail, and therefore the focusing operation effected before becomes completely meaningless.
In order to solve this problem it is conceivable to allow the focusing and searching operations to proceed in parallel. But then the high speed movement of original images would impair focus detection or result in a detection error.
(b) Microfilms include the rolled type and microfiche type, and interchanging between the two types is usually carried out by changing the entire microfilm carrier. Since a different type of carrier results in a different focal point, a focusing operation must be carried out each time the carrier is changed. No problem arises if a focusing operation is carried out after the carrier is changed. However, when the carrier is changed during a focusing operation, the latter becomes meaningless and an operational error may take place.
(c) Original images are not always recorded on a microfilm in a uniform size, but may be recorded in various sizes such as B4, B5 and so on and in different magnification ratios. This requires the projecting lens to be changed frequently, which entails a similar problem in relation to the focusing operation. That is, when the projecting lens is changed during the focusing operation, the latter loses its meaning entirely and an operational error may take place.